Lapping is a well established process for finishing the tooth surfaces of bevel gears. It is a process that provides an economical alternative to other hard finishing processes for bevel gears and it has been used in all areas except for some aircraft applications.
In the lapping process, a pinion and ring gear are mounted, via appropriate workholding equipment, to respective spindles in a lapping machine that has the same basic design as a testing machine. In most instances of rolling of the gearset, the pinion is the driving member and the ring gear is braked. The gears are rolled in mesh and lapping compound, which can be a mixture of oil (or water) and silicon carbide or similar abrasive, is poured into the meshing zone. Examples of lapping and/or testing machines can be found in U.S. Pat. Nos. 3,099,901 to Hunkeler; 3,142,940 to Rebeski; 3,717,958 to Ellwanger et al.; or, 5,609,058 to Gnadt et al.
Most lapping and testing machines have three degrees of freedom available for realizing relative motion between a ring gear and pinion. The first freedom being relative movement in the direction of the ring rear axis which shall be referred to as direction G or the G axis, the second freedom being relative movement in direction of the pinion axis which shall be referred to as direction H or the H axis, and the third degree of freedom being distance between the ring gear and pinion axes which shall be referred to as direction V or the V axis. The direction V is also known as the "hypoid offset."
In lapping or testing processes, relative movement in the V and H directions effect positional changes in the contact pattern of the members of the gearset, in effect modifying the contact pattern. Lapping involves rotating the gear members in mesh with contact at a desired position on the tooth surfaces. Thus, the members are located at particular V and H positions along with a particular G axis position to effect the desired backlash.
Typically, the V, H and G movements each have an effect on both the lengthwise and depthwise position of the localized tooth contact pattern, the primary effect of the V-axis movement being on the relative lengthwise position of the contact pattern, the primary effect of H-axis movement being on the relative depthwise position of the contact pattern, and the primary effect of G-axis movement being on the backlash.
As the gear set is lapped, contact is shifted toward one of the outer (heel) or inner (toe) portions of the tooth surface by changing the V and H settings as necessary to effect such a shifting of the contact position. As V and H are changed to effect the shifting, the G axis position must also be changed to maintain the desired backlash. When the desired heel or toe position is reached, V and H axes positions are again changed to shift contact to the other of the heel or toe positions with the changing V and H positions being accompanied by an appropriate G-axis change to maintain backlash. The contact position is then returned to the beginning position.
To date, the structure of lapping machines usually has been similar to the construction principle as bevel gear cutting and grinding machines except that in most lapping machines, the shaft angle is permanently set to 90.degree.. Thus, lapping machines have one less degree of freedom than cutting and/or grinding machines.
However, such similarities to cutting and grinding machines results in many machine elements (for example, columns, slides and ways) lying between the ring gear and pinion members which introduces unwanted and uncontrolled compliance into the lapping process. Furthermore, with an increasing number of machine elements between the gearset members, the distance between the gearset members and the machine base undoubtedly increases, thus lessening the beneficial stiffness and stability effects provided by close proximity of the gearset members to the machine base.
It is an object of the present invention to provide a lapping machine which eliminates many of the machine elements between gearset members thereby enhancing machine stability.
It is a further object to provide a high speed lapping process including a method to introduce lapping compound during the high speed lapping as well as monitoring vibration of a gearset during lapping as a means to signal optimal conditions of the lapped gearset.
These and other objects and advantages of the present invention will appear more clearly from the following description and the accompanying drawings.